By the end of this module you will understand the assumptions and dynamics of the exponential growth model and have an understanding of how ecologists use this model to explore population dynamics, such as the growth of a reindeer population on an island off the state of Alaska.

Overview

When populations are small and resources abundant individuals can, on average, consume large amounts of resources and ultimately leave many offspring. Because the health of organisms may be high with abundant food their death rates may also be low. Therefore, birth rates may greatly exceed death rates leading to rapid population growth.

Likewise, we might find times when populations are in decline with death rates exceeding birth rates, with the potential for a population to become extinct. For now we will assume that the growth rate of a population does not change while realizing this assumption probably will not hold for long periods of time.

Sample problem

In 1911 the United States government placed 25 reindeer on St. Paul Island in the Pribilof Island chain, Alaska (see satellite image), with the intention of providing a food source for the native people. Of the 25 reindeer 21 were females. The population grew for many years, despite harvests. Can we use the exponential growth rate model to understand and predict changes in this population?

(Satellite image of the Aleutian Islands and the Alaskan peninsula. Courtesy NASA.)